The present invention relates a liquid crystal device, and in particular to a polymer dispersed liquid crystal device.
Polymer dispersed liquid crystals (PDLC), consisting of micron-sized LC droplets dispersed in a polymer matrix, are a promising electro-optic material for displays, light switches, and tunable-focus lenses because of their polarization independence. Phase separation, is an important process affecting the electro-optic properties of PDLC. In a conventional PDLC, the formed droplets, each about the size of a visible wavelength, are randomly distributed in the polymer matrix. Typically, the LC and monomer mixture is sandwiched between two indium-tin-oxide (ITO) glasses without any surface treatment. After photo-induced phase separation, the droplets are formed and their sizes vary.
In general, the operation of PDLC depends on the application of voltage. For normal mode PDLC, when a sufficient voltage is applied, the PDLC becomes transparent and allows light to pass, while the PDLC is opaque and scatters light without an applied voltage. For reverse mode PDLC, the transmittance-driving condition is just reversed. In other words, PDLC windows are based on the ability of the nematic director of the liquid crystal droplets to align under an electric field. The PDLC is suitable for an electro-optic material of a light modulation device used in high-brightness projectors, because it exhibits high optical transparency without a polarizer.
However, due to micro-sized LC droplets, a relatively large cell gap is necessary. Besides, liquid crystals are surrounded by polymers, so the operating voltage for initiating liquid crystal becomes relatively high. In general, for different composition substrates, the operating voltage ranges from 10 to 200 V.